Hint 1: the U is also a stand off spacer.. the 4 nuts and the 2 acorn nuts go on so as 2 nuts push the plasti-dipped plate against the fork blade.

Backing Out the Other 2 nuts clamps the rack rear corner between those 2 nuts and the acorn nuts on the outside ..

Doing that the 2 sides of the rack are parallel to each other , and there is sufficient space for the Bag mount hooks at the top edge, even at the back.